1. Field of The Invention
The plasticizer technology of today is a hybrid of art and science, formulated and derived from the discoveries by various primitive people. For example, Neat's-foot and sperm oil applied to leather were plasticizers utilized by early artisans. Similarly, the modern plasticizer industry evolved as a result of surface coatings. For example, when a resin used in a varnish left a film that was inelastic and too brittle it was modified with a drying oil or other material which would impart to it the requisite property of toughness by giving it the right amount of plasticity. The term "plasticizer" as used herein is a softner or substance which when incorporated in a material (usually a plastic or elastomer) increases its flexibility, workability or distensibility.
A plasticizer may reduce the melt viscosity, lower the temperature of a second-order transition, or lower the elastic modulus of the material with which it is admixed. Second-order transition temperatures may be determined by plotting any temperature dependent property of a material, such as density or refractive index, against temperature. The transition temperature, which is believed to be identified with the onset of rotational freedom within the material's macromolecules, may be located and determined by a sharp change of curvature. Since plasticization lowers this temperature by reducing interchain barriers against rotation, it follows that a comparison of second-order transition temperatures on polymer plasticized compositions that are equivalent at room temperature affords a means of evaluating the temperature performance of plasticizers.
2. Description of The Prior Art
The plasticization of ethylene-acrylic acid copolymers is old and is described, for example, in U.S. Pat. No. 3,361,702 issued to Wartman et al., on Jan. 2, 1968, entitled Ethylene-Acrylic Acid Copolymers Plasticized With Polyols. In particular, glycols, glycerols and the like are described as suitable for use as melt index, stiffness, processability, glass transition temperature and resiliency improvers when added to ethylene-acrylic acid or ethylene methacrylic acid copolymers. As can readily be determined from the foregoing there is an ongoing search for new and superior plasticizers for various polymers and copolymers. Similarly, in U.S. Pat. No. 3,464,949, also issued to Wartman et al., on Sept. 2, 1969, entitled Ethylene-Acrylic Acid Copolymers Plasticized with Adducts of Alkylene Oxides and Amines, adducts of alkylene oxides and amines are used as plasticizers in said copolymers.